In recent years, a noise cancelling (noise reduction) technology has been widely developed. The noise reduction technology is broadly divided into two methods including a Feedforward (FF) method and a Feedback (FB) method. In many cases, these methods are appropriately used in accordance with a targeted noise.
On the other hand, there exists an idea of combining these noise reduction technologies. For example, Patent Literature 1 described below discloses a technology of enhancing a noise reduction effect in headphones by combining the FF method and the FB method.